/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.io;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import com.google.common.base.Preconditions;

/**
 * An InputStream that limits the number of bytes which can be read.
 * 
 * @author Charles Fry
 * @since 2009.09.15 <b>tentative</b>
 */
public class LimitInputStream extends FilterInputStream {

    private long left;
    private long mark = -1;

    /**
     * Wraps another input stream, limiting the number of bytes which can be
     * read.
     * 
     * @param in
     *            the input stream to be wrapped
     * @param limit
     *            the maximum number of bytes to be read
     */
    public LimitInputStream(InputStream in, long limit) {
        super(in);
        Preconditions.checkNotNull(in);
        Preconditions.checkArgument(limit >= 0, "limit must be non-negative");
        left = limit;
    }

    @Override
    public int available() throws IOException {
        return (int) Math.min(in.available(), left);
    }

    @Override
    public void mark(int readlimit) {
        in.mark(readlimit);
        mark = left;
        // it's okay to mark even if mark isn't supported, as reset won't work
    }

    @Override
    public int read() throws IOException {
        if (left == 0) {
            return -1;
        }

        int result = in.read();
        if (result != -1) {
            --left;
        }
        return result;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (left == 0) {
            return -1;
        }

        len = (int) Math.min(len, left);
        int result = in.read(b, off, len);
        if (result != -1) {
            left -= result;
        }
        return result;
    }

    @Override
    public void reset() throws IOException {
        if (!in.markSupported()) {
            throw new IOException("Mark not supported");
        }
        if (mark == -1) {
            throw new IOException("Mark not set");
        }

        in.reset();
        left = mark;
    }

    @Override
    public long skip(long n) throws IOException {
        n = Math.min(n, left);
        long skipped = in.skip(n);
        left -= skipped;
        return skipped;
    }

}
